Washington: Scientists have built a tractor beam that can repel and attract objects, using a hollow laser beam that is bright around the edges and dark in its centre.

This first long-distance optical tractor beam has been able to move particles one fifth of a millimetre in diameter a distance of up to 20 centimetres, around 100 times further than previous experiments and requires only a single laser beam.

Professor Wieslaw Krolikowski, from the Research School of Physics and Engineering at The Australian National University, said that demonstration of a large scale laser beam like this is a kind of holy grail for laser physicists.

The beam could be used, for example, in controlling atmospheric pollution or for the retrieval of tiny, delicate or dangerous particles for sampling and researchers added that they have devised a technique that can create unusual states of polarisation in the doughnut shaped laser beam, such as star-shaped (axial) or ring polarised (azimuthal).